Influence of Copper Doping on the Structural, Optical and Dielectric Properties of Potassium Acid Phthalate (KAP) Single Crystals

Abstract

Good quality and optically transparent single crystals of pure and Cu doped potassium acid phthalate (KAP) were grown by slow evaporation technique. Powder X-ray diffraction suggests that the both the pure and Cu doped KAP crystals are crystallized in the orthorhombic structure. Inductively coupled plasma-optical emission spectrometric studies confirmed the Cu²⁺ ion doping into KAP crystals. The functional groups and the effect of moisture on the doped crystals were analyzed with the help of a FTIR spectrum. The pure and doped potassium hydrogen phthalate single crystal shows good transparency in the entire visible region, which is suitable for optical device applications. Thermogravimetric analysis studies reveal that the purity of the sample and no decomposition is observed below the melting point. Microhardness studies reveal that the Cu²⁺ doped crystals have higher hardness values than that of pristine KAP. Dielectric constant value of Cu²⁺ doped KAP at 100 Hz was found to be extensively higher than that of pristine KAP. Second harmonic generation efficiency of 0.3 mol% Cu²⁺ doped KAP crystal was found to be 1.85 times [31 mV for potassium dihydrogen phosphate (KDP) and 55 mV for 0.3 M Cu²⁺ doped KAP] that of KDP crystal. This is much higher when compared to that of undoped KAP crystal (15 mV). This result confirms that Cu doped crystals are suitable for device fabrication in nonlinear optical applications.

Graphical Abstract

Dielectric constant versus log frequency measured at 40 °C of pure and Cu doped KAP crystals. Dielectric constant value of Cu²⁺ doped KAP at 100 Hz was found to be extensively higher than that of pristine KAP. Cu²⁺ ions has strong influence in structural, optical, dielectric and nonlinear optical properties of potassium acid phthalate (KAP) single crystals.